Retracting cutter

ABSTRACT

A knife is disclosed having a self-retracting, adjustable blade. The handle of the knife has two pieces which when compressed expose the blade for use.

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/746,997 filed Aug. 19, 1991, now U.S. Pat. No. 5,208,983.

FIELD OF THE INVENTION

This invention relates to cutting tools and more particularly to handheld tools with retractable blades.

BACKGROUND OF THE INVENTION

Knives date from the Stone Age and are important to the present day.Exposed blades on knives can be a hazard and thus sheaths were developedto cover the blade. As early as the Roman Empire folding knives weredeveloped. Such folding knives are called pocket or army knives andprovide a safe means of carrying and storing bladed tools.

U.S. Pat. No. 2,037,914 discloses a knife offering razor sharpness. Suchknives are now known as utility, shop or trimming knives. A variety ofthese knives have been developed including ones with retractable bladessuch as U.S. Pat. No. 4,733,734, which employs a button for retractingthe blade. Crosses between pocket and utility knives are known.

A scalpel is a small lightweight knife used to cut tissue duringdissection or surgery. For such use it is essential to control the depthof the cut since the number of layers or thickness of tissue to be cutvaries. For a surgery, it is desirable to have a blade thatautomatically retracts to protect health care personnel against serumtransmitted diseases such as AIDS and hepatitis B. Most scalpels use adisposable blade and holder. One such holder is described in U.S. Pat.No. 4,930,220, incorporated herein by reference.

Coupon cutters, designed to cut sections from newspapers and magazinesalso require control of the blade depth to avoid cutting extra pages.Additionally, it is desirable that such cutters be small enough to becarried about in a pocket or purse. Hook coupon cutters place a guidebetween the blade and the layer that is not to be cut. Others have avery small exposure of a nonadjustable blade.

Presently, sheathed blades require a specific movement by the user suchas folding, unfolding or sliding a button. Operation takes consciouseffort on the part of the user and sheathing mechanisms addsubstantially to the cost of manufacture.

However, the inventor is unaware of a self-retracting, adjustable depthknives of reasonable cost.

DESCRIPTION OF THE INVENTION

The subject invention of the application is a self-retracting,adjustable knife which operates by displacement due to compression. Thehandle of the knife is comprised of two legs of unequal length. The legsare attached to each other at one end and a blade is located at theunattached end of the longer arm. At least one of the legs is made froma resilient material. The longer leg is curved so that the blade'scutting edge rests against the shorter leg. The shorter leg is lesscurved, preferably straight. To use the knife the legs of the handle arecompressed between the digits of the user, causing a displacement of thelegs. If the longer leg is resilient, compression toward the shorter leglengthens the effective length of the longer leg. The effective lengthrefers to the length of a chord from the point of attachment to theunattached end of the shorter leg or the blade edge of the longer leg.If the shorter leg is resilient, compression into the curve of thelonger leg shortens the effective length of the shorter leg. At rest,that is, not compressed, the effective length of the long leg is lessthan the effective length of the short leg, and the blade is retractedand unexposed. Under compression, the effective length of the long legexceeds the effective length of the short leg, and the blade is exposedfor use. The amount of blade exposed can be adjusted by controlling theamount of compression. When the compression is released, the knifeautomatically resumes its original safe position.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a retracted utility knife in accordancewith the invention.

FIG. 2 is a perspective view of the knife shown in FIG. 1 in a displacedor exposed position.

FIG. 3 is a side view of the knife shown in FIG. 1.

FIG. 4 is a side view of the knife as shown in FIG. 2

FIG. 5 is a perspective view of a retracted utility knife having anintegral blade in accordance with the invention.

FIG. 6 is a perspective view of the knife shown in FIG. 5 in a displacedor exposed position.

FIG. 7 is a front perspective view of a scalpel having a in theretracted position in accordance with the invention.

FIG. 8 is a perspective of the removable stop 7 shown in FIGS. 7 and 10.

FIG. 9 is a front perspective view of a commercially available scalpelblade.

FIG. 10 is a back perspective view of the scalpel shown in FIG. 7.

FIG. 11 is side view of a scalpel having a screw to control the depth ofthe cut.

FIG. 12 is a side view of a knife with a roller.

FIG. 13 is a detail of a tab for attachment for a scalpel blade.

FIG. 14 is a perspective view of a detail of a tension holder for ablade before bending.

FIG. 15 is a perspective view of a detail of a knife showing thecompleted tension holder with disposable blade

FIG. 16 is a side view of the detail shown in FIG. 15.

FIG. 17 is a perspective view of a combination knife-clip.

FIG. 18 is a side view of a combination knife-clip.

FIG. 19 is a perspective view of a pen.

FIG. 20 is a side view of a knife having legs formed with straightsegments.

FIG. 21 is a top view of a retracting cutter having a sliding blade heldby a key block.

FIG. 22 is a side view of the cutter of FIG. 21.

FIGS. 23 A, 23 B, and 23 C are top, side and bottom views of the keyblock for the cutter of FIG. 21.

FIG. 24 is a top view of the cutter of FIG. 21 with the top removed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 through 4 show a self-retracting cutting tool having a rigid,straight leg 1 and a longer, resilient bent or bowed leg 2 attached atone end 3. Both legs are angled at the unattached end 4 to facilitateholding the tool at an angle. A blade 5 is located at the unattached endof the longer leg 2. Although the blade and leg may be integral, it ispreferable some means of attachment 6 be used. The length of the longerleg 2 must be such that when fully bowed or bent, that is, in a restingstate, no line from a point on attached end of the longer, resilient leg2 to a point on the blade 5 is greater than a corresponding line fromthe same point of attachment to a corresponding point on the unattachedend of the short leg 1 thus shielding the blade. In other words, theeffective length of the longer leg is less than the effective length ofthe shorter leg at rest. Also, in this position the cutting edge ofblade 5 is pressed against the shorter, rigid leg 1, so the blade doesnot catch on an unintended object. Suitable materials for resilient legsare spring metals such as steel, brass, and aluminium, or a resilientplastic such as polyethylene or polypropylene. Suitable materials forthe rigid legs are steel, brass, aluminium, plastic or ceramic. Bothlegs may be made of the same material, however, it is preferable thatthe thickness of shorter leg 1 be greater than the thickness of thelonger leg 2 for added resiliency of the longer leg 2. Commerciallyavailable blades, such as breakaway blades available from Stanley toolsmay be attached by a cement such as super-glue, solder, spotwelding, bya screw, molded in, by a tab such as shown in FIG. 13, by the tensionholder disclosed in FIGS. 14, 15 and 16, or any convenient method whichdoes not obstruct the use of the knife. Since most blades are flat, thesection of the longer, resilient leg 2 resting against the blade 5 isflat. In use the legs are compressed between the user's digits,displacing the longer leg 2. When compressed the effective length of thelonger, resilient leg 2 (that is from the attachment point along thecurve to the cutting edge of the blade) must be greater than theeffective length of the shorter, rigid leg 1. As the longer leg 2 isdisplaced, the blade 5 is exposed for use. If light pressure is used,the blade 5 is displaced only slightly, allowing for a shallow cut,heavier pressure exposes more of the blade for a deeper cut. The depthof the cut is adjusted by varying the amount of compression. Whencompression is released, the blade 5 automatically retracts to its safeposition.

FIGS. 5 and 6 show a knife made from one piece of material. In thisembodiment the blade 5 has been formed from the unattached end of thelonger leg 2. Tapering the material results in a more resilient leg withless thickness than the rigid leg. If steel is used, the blade edge canbe heat treated to retain sharpness.

The relationship between the amount and placement of the bowing orbending of the curved leg 2 and the amount of blade 5 exposed can beestimated by inscribing a right triangle having a height from the pointof pressure on the curved leg to the nearest point on the straight leg,having a base along the straight leg from the blade to the point formedby the intersection of the height with the base, and having a hypotenusefrom the point of pressure to the blade. As the height is decreased, bypressure, and the hypotenuse remains constant, the base of the triangleincreases. The change in height of the triangle defines the displacementat the pressure point, and the change in the base of the triangledefines the displacement of the blade. The ratio of blade displacementto displacement of the pressure point can be approximated by the ratioof the difference between the sines to the difference between thecosines of the angles formed by the first triangle leg and thehypotenuse at the initial and final positions. It has been found thatknives having a blade to pressure point displacement ratio of 1:4 aresatisfactory. The amount of bending or bowing may be adjusted to give adegree of control of depth suitable for the desired application. Metalcan be bent for the knife on a bending machine such as described in U.S.Pat. No. 5,007,269 incorporated herein by reference. Alternatively theknife could be molded from a resilient plastic. By placing a blade inthe plastic, the plastic could serve as a stop to further control thedepth of the cut.

The scalpel shown in FIGS. 7 and 10 has a stopping device for precisecontrol of displacement and therefore the depth of a cut. The stoppingdevice 7 is a clip which slides on the leg of the scalpel and can bepreset to a particular displacement. The clip can be easily removed.Such displacement control devices can be used with other embodiments.The scalpel is designed to take advantage of commercially availableblades such as those shown in FIG. 9. In this embodiment, the longer leg2 is tapped for a screw 6 which fits through opening 8 in the blade.Access to the head of the screw 6 is made via an aperture 9 in the rigidleg 1. Any suitable means of attaching blades could be used such as tab,or holder such as described in U.S. Pat. No. 4,930,220. The preferredmaterial for scalpels is stainless steel. The scalpel of FIG. 10 isprovided with textured legs to provide a better grip.

The scalpel of FIG. 11 has a similar means of securing 6 the blade 5 tothat in FIGS. 7 and 10, but the means of controlling the amount ofdisplacement is a screw 11.

The knife shown in FIG. 12 has a roller 12 attached to the shorterleg 1. This wheel reduces friction when the knife is used on softmaterial such as rubber or tissue.

The detail in FIG. 13 shows a tab 6 fop attaching a commerciallyavailable scalpel blade 5 as shown in FIG. 9. The tab has a "T" shapedcross section. The cross bar of the T is slightly narrower than thewidth of the widest part of the slot 8 in the blade 5. The stem issubstantially the same as the width of the narrow section of the slot 8in the blade 5.

FIGS. 14 and 15 show a blade holder based on tension and method ofmaking the same. An aperture 13 is drilled or stamped in the unattachedend of the longer leg 2. The leg 2 is then bent to form a U having aridge 14 at the upper end. The blade 5 is then installed by pressingagainst a wood or a soft metal to force it into the aperture. Upon beingforced in the blade will bend slightly. The blade 5 can be removed withpliers.

The knife can be modified to combine with other useful objects such as apaper clip, pocket clip, bookmark, money clip or tweezers. FIGS. 17 and18 show one such modification for clipping to a lapel or the top of ashirt pocket 16 or as a business card holder. In the knife shown, theknife is clipped with a outer resilient handle 15, which may beremovable. The handle also serves to stiffen the shorter leg 1.

The knives thus described have all shown legs which have a roundedcurve. However, as shown in FIG. 20, straight segmented curves will alsowork. The shorter less curved leg 30 (in this case straight) is fastenedat its upper end 32 to the longest leg upper end 34. The longer leg hastwo straight segments 36 and 38 forming an angle 0. Pressure on thelonger leg extends the blade 40 for use. Of course the longer leg mayemploy several straight segments or combinations of straight and roundedcurves.

FIGS. 21 and 24 show an alternative scalpel, in which the longer leg isformed by a curved section 52, a key block 50 and a scalpel blade 46.The shorter less curved leg 56 has a slot 66 at the upper end, anaperture 62 for a depth control screw 68, and a groove 58 for retainingand guiding a scalpel blade 46. The groove 58 has a hole for easieraccess to the blade 46. The slot 66 in the upper end receives an upperlip 70B of the upper leg curved section 52 To further secure the section52, a screw 54 passes through the leg into an aperture 64 in the shorterleg 56. The scalpel blade 46 lies loosely in the groove 58 betweenridges 44. To secure the tip of the blade, a plate 42 covers the lowersection of the groove and is held in place by screw 72. A longitudinalridge 80 of the key block 50 is placed in the scalpel blade slot 48. Agroove 70 on the opposing side of the key block 50, engages a second lip70B of the upper leg curved section 52. This arrangement provides foreasy blade replacement and accurate depth control.

Although the tool thus far described is a knife, the retracting handlecould be modified for other tools such as a punch, writing implement,string cutter, micro probe or gauge. If the tip of the tool cannot slideover the surface of the shorter leg, the longer leg could be grooved ornotched to allow for protection of the tool. FIG. 19 shows a pen with aflexible refill 16 attached to the longer leg 1 and a groove 17 toprotect the pen point 18.

A string cutter could be formed by cutting a notch in the shorter leg toguide the string.

The tools disclosed in this invention are inexpensively manufactured,easy to use, and require no complicated adjustments. Automaticretraction ensures the tool is safely out of the way when not in use.These tools could be carried in the purse or pocket of the user, beinghandy for clipping items from newspapers, plastic unopened seals fromcontainers, bubble wrap, leather, and layers of tissue.

What is claimed is:
 1. An adjustable self-retracting instrumentcomprising:(a) a primary functional section of said instrument; (b) afirst curved leg having upper and lower ends, said section being locatedat the lower end of said first leg; and (c) a second shorter less curvedleg having upper and lower ends, wherein at least one leg is made from aresilient material, said second leg being attached to said first leg atthe upper end and resting against said section, whereby when said legsare compressed together said section extends beyond said second leg. 2.The instrument of claim 1 wherein said section is chosen from the groupconsisting of points, blades and probes.
 3. The instrument of claim 1wherein said instrument is a knife and said section is a blade.
 4. Theinstrument of claim 1 wherein said first curved leg has at least onestraight section.
 5. The instrument of claim 4 wherein said leg has twostraight sections which form a nonstraight angle.
 6. The instrument ofclaim 1 wherein said first leg further comprises:a blade; a key block;and a curved section.
 7. The instrument of claim 6 wherein said bladefurther comprises:a scalpel blade having a slot, and said key block hasa projection for engaging said slot.
 8. The instrument of claim 7wherein said key block has a groove and said curved section has at leastone lip, said groove receiving said lip.
 9. The instrument of claim 8wherein said curved section has two lips and said second leg has anopening for receiving said lips.
 10. The instrument of claim 6 whereinsaid second leg has a slot for resting said blade in.
 11. The instrumentof claim 10 wherein said second arm further comprises a plate forcovering a portion of said blade slot.
 12. The instrument of claim 6wherein said curved section is detachable.
 13. The instrument of claim12 wherein said curved section has at least one lip and said second leghas an opening for receiving said lip.
 14. The instrument of claim 6further comprising:means for controlling the depth of a cut made by saidblade.
 15. The instrument of claim 14 wherein said means furthercomprises:a threaded controller located in said second leg.
 16. Theinstrument of claim 6 wherein at least one leg is textured
 17. Theinstrument of claim 6 wherein said lower ends of said legs are angled tofacilitate holding said knife at an angle.